1. Field of the Invention
Drilling rigs use blowout preventers (BOPs) to shut in a well during emergencies and for other purposes. The BOP operating system needs to be reliable in order to protect lives, the environment, and property. This invention relates to an improved BOP operating system and a quick dump valve. The quick dump valve includes a shuttle that has some structural similarity to shuttle valves used for control functions in prior art BOP operating systems. Specifically, the quick dump valve has some structural similarities to the Low Interflow Hydraulic Shuttle Valve which is the subject of a pending U.S. patent application Ser. No. 09/452,594 filed on Dec. 1, 1999 and a pending U.S. patent application Ser. No. 09/653,415 for a Pressure Biased Shuttle Valve filed on Sep. 1, 2000, both of which are incorporated herein by reference. Gilmore Valve Co. is the owner of these two pending U.S. Patent Applications, the present patent application for BOP Operating System with Quick Dump Valve and other U.S. patents for shuttle valves including U.S. Pat. Nos. 3,533,431 and 4,253,481. However, the present invention is structurally distinct from these prior art shuttle valves and it performs a different function as discussed below.
2. Description of the Prior Art
Subsea wellhead systems are often relied upon during deep-water exploration for oil and natural gas. The subsea wellhead system includes a stack of BOPs. Annular BOPs are actuated on a routine basis to snub or otherwise control pressure during normal drilling operations. Other blowout preventers, such as blind rams, pipe rams, and shear rams will also be included in the stack on the subsea wellhead. When these types of rams are actuated, operations in the well cease in order to control pressure or some other anomaly. Blind rams, pipe rams, shear rams and annular preventers are periodically functioned and tested to make sure that they are operational.
BOPs are tested periodically to ensure that they will function in emergencies and in other situations. Prior art subsea BOP operating systems include control pods, the lower marine riser package (LMRP), the BOP stack and interconnecting hoses and pipes. From time to time it may be necessary to perform an emergency disconnect of the LMRP from the BOP stack, for example, if a drill ship drifts off station or if a storm approaches. If it is necessary to make an emergency disconnect of the LMRP from the BOP stack, it will be necessary to close the shear rams. During the closing sequence, hydraulic fluid is forced through pipes or hose, a shuttle valve and additional segments of pipes or hose before it finally reaches the directional control valve vent port on the control pod where it is vented to the ocean. This circuitous hydraulic vent path results in a high differential pressure, which decreases flow of control fluid through the close side of the operating system. The decreased flow consumes valuable seconds, and as such, increases the time required to close the shear rams and disconnect the LMRP from the BOP stack. In prior art BOP operating systems, pilot operated check valves or conventional sub-plate mounted (SPM) poppet valves were used to vent this fluid during the closing sequence. These prior art vent devices rely upon springs or pilot pressure to operate properly.
The present dump valve for use in the improved BOP operating system utilizes a ported shuttle that automatically shifts with the direction of hydraulic pressure to either expose or seal the vent port in the valve. The present dump valve has two positionsxe2x80x94vent and open. It has several advantages over the prior art due to its location in the BOP operating system and its design. These advantages occur when the valve is in both the vent and the open positions as discussed below. The present dump valve is a much simpler design than the prior art pilot operated check valves and conventional SPM valves.
The present dump valve and improved BOP operating system are designed to reduce hydraulic shock and vibration, to reduce the incidence of hose collapse on both the close side and the open side of the system, to facilitate installation and maintenance, and to shorten the emergency disconnect sequence of the LMRP from the BOP stack. In some prior art systems, hydraulic shock and vibration would sometimes accompany the closing function.
In the improved BOP operating system the dump valve of the present invention is located at or near the open port of the BOP. During the closing sequence in the improved BOP operating system, the present dump valve is shifted to the vent position. In this position fluid is vented from the BOP operating system. When it is time to open the shear rams, fluid flow reverses through the dump valve and it moves to the open position. In the open position, the vent is closed allowing fluid to move through the open port into the BOP to open the rams.
Some BOP hoses may collapse in deep water when subjected to high velocity flows of hydraulic fluid resulting from functioning of the BOPs with large capacity operators. Hose collapse is, of course, undesirable. The present dump valve and the improved BOP operating system are designed to reduce flow velocities in the control system, and thereby reduce the incidence of BOP control hose collapse. In the improved BOP operating system, the dump valve is positioned at or near the open port on the BOP to vent fluid from the system during the closing sequence. Because the dump valve is located at or near the open port on the Ram""s BOP, this high velocity fluid is vented and does not pass through the open side hose. The control hoses on the open side of the BOP will, therefore, be less prone to collapse because they are no longer exposed to the hydraulic shock and negative pressure waves caused by high velocity flow of fluid when the BOP rams are being closed.
When the rams are being opened, the dump valve also acts as a dampener to reduce the incidence of hose collapse on the close side of the operating system. In a preferred embodiment, when the rams are functioned open, fluid passing through the dump valve is restricted because the orifice through the dump valve is smaller than the inside diameter of the hose leading to and exiting from the dump valve. This flow restrictor will effectively slow down the velocity of the fluid entering the BOP rams. In turn, the velocity of the exhausting fluid from the close side will be reduced to a rate that reduces hydraulic shock and therefore reduces the incidence of hose collapse. In some prior art BOP operating systems, it may take as much as 20 seconds to close and open the rams. The improved BOP operating system with quick dump valve should allow the rams to close in approximately 5 to 15 seconds; however, it may take more than 30 seconds for the rams to open.
Maintenance on prior art BOP operating systems is sometimes lengthy and expensive. The present dump valve is smaller and lighter than conventional SPM valves or pilot operated check valves, which will facilitate valve installation reliability and maintenance.
The improved BOP operating system with quick dump valve should reduce the amount of time it takes to make an emergency disconnect of the LMRP from the BOP stack. In prior art BOP operating systems when it was necessary to close the rams, fluid was forced through a length of hydraulic hose, a shuttle valve and additional segments of tubing or hose before it finally reached the directional control valve vent port on the control pod. This circuitous hydraulic vent path on the close side of prior art operating systems results in a high differential pressure, which decreases flow of control fluid when the rams are being closed. The decreased flow consumes valuable seconds and, as such, increases the time required to close the rams and disconnect the LMRP from the BOP stack. Positioning the quick dump valve at or near the BOP Ram""s open port will substantially shorten the hydraulic vent path and reduce the differential pressure. All of these features will reduce the amount of time required to close the BOP rams during an emergency and thus speed up the disconnect of the LMRP from the BOP stack.
The quick dump valve uses a ported shuttle design that shifts to either expose or seal off the vent port in the valve. When the BOP is being closed, the shuttle moves to the vent position allowing fluid to be vented from the improved operating system. This vent function which is located at or near the BOP prevents high velocity fluid from passing through the open side hose thus reducing the incidence of hydraulic shock, vibration and hose collapse.
When the BOP is being opened, the shuttle in the dump valve moves to the open position allowing fluid to pass through the dump valve and into the BOP. A flow restrictor is positioned in the shuttle, which acts as a dampener to reduce hydraulic shock, vibration and the incidence of hose collapse on the close side of the BOP rams. While the BOP is being opened, it is important that the shuttle achieve a good seal to prevent fluid from escaping to vent. The diameter on the supply side of the shuttle is larger than the diameter on the BOP side which results in more force being applied to the seals to prevent unwanted fluid from escaping to vent while the BOP is being opened.
In some situations, it is desirable to prevent fluid from flowing to supply when fluid is escaping to vent while the BOP is being opened. In the first alternative embodiment, a ball check valve, is positioned in the shuttle to block fluid flow from the BOP to supply when the dump valve is in the vent position. In the first alternative embodiment, the diameter on the supply side of the shuttle is larger than the diameter on the BOP side, which results in more force being applied to the seals to prevent unwanted fluid from escaping to vent while the BOP is being opened.
In the second alternative embodiment, a ball check valve is positioned in the shuttle to block fluid flow from the BOP to supply when the dump valve is in the vent position. In the second alternative embodiment, the diameter on the supply side of the shuttle is the same diameter as in the BOP side. The cracking pressure of the check valve results in the differential pressure and force required to energize the metal to metal face seal. Differential area was utilized to accomplish this in the alternative and first alternative embodiment.
In the third alternative embodiment, there is no internal check valve and the diameter on the supply side of the shuttle is the same diameter as on the BOP side. In the third alternative embodiment soft seals are used on both sides of the shuttle to achieve a seal. These seals may be located in either the shuttle or adapters.